The present invention relates to a new and improved concept in oil, gas or water drilling systems and offers significant economies in equipment acquisition, well drilling and in the cost and time required to drill and bring into production fluid producing wells. The invention is suitable for use in environments and areas that would otherwise preclude fluid mineral development due to population congestion or ecological considerations. The system of the invention is adaptable for use in either on shore or offshore oil, gas or water well drilling with advantageous efficiencies in economies for both forms of application. While it is to be understood that the invention has utility in drilling for any type of subsurface fluid, the embodiments discussed herein are approached from the standpoint of drilling for crude oil.
In offshore applications, wells are conventionally drilled from a platform that is mounted on a substructure that extends from the floor of the ocean to a level located above a designated storm wave elevation. Conventional structures usually consist of a series of crossed braced steel legs, Alternatively, drilling operations are conventionally conducted from semi-submersible floating platforms.
These conventional structures employ a single drilling derrick and machinery located on the platform for drilling a single well at any particular time. The platform usually contains living quarters for the drilling and operating crews. A plurality of wells may be drilled from such platforms by slant drilling techniques, so that the locations wherein the wells intersect the underground oil production formations are laterally displaced from the platform by hundreds or thousands of feet. Furthermore, the wells must be drilled serially, that is one at a time. As each well is completed, the derrick and drilling equipment are moved to a new location on the platform where a subsequent well is drilled. Hence, if 30 wells are involved in the drilling program, it normally takes on the order of 60 months to complete all wells. Currently, drilling platforms normally cost from $30,000 to $50,000 per day to operate, so that the total cost for just rig drilling time runs from 54 to 90 million dollars. Full production from conventional platforms can not be realized until the final well is completed, which, as previously stated, is of the order of 60 months.
Conventional land based wells likewise involve the erection of a derrick above a well drilling location to drill a single well at a time. Drilling pipe sections are lifted into position and lowered to be joined with existing drilling pipe sections. When pipe is to be withdrawn for changing bits, stands of pipe (usually three drilling pipe sections linearly joined together) are withdrawn from the well using the derrick structure. Such conventional drilling structures involve the use of an unsightly derrick and are designed to drill but a single well at a time. These disadvantageous features have virtually precluded conventional well drilling apparatus from being located in highly urbanized locations because the aesthetic appearance of such conventional drilling rigs is unacceptable to the surrounding community, and because the economic realities of drilling a single well in each of several different area locations on land of high real estate value defeat the profitability of such undertakings.
Accordingly, it is an object of the present invention to provide a well drilling apparatus that is capable of drilling a plurality of wells concurrently. Utilizing the four well drilling configuration depicted herein, a drilling program could be completed in sixteen months as contrasted with the more conventional period for a well drilling program of sixty months. The resulting savings at current rates amount to from 40 to 65 million dollars. As significant as the savings are, they still do not entirely reflect the economic advantage of producing oil in time then would otherwise be possible. With increasing dependence on foreign oil resources, this feature may well be the most important aspect of the present invention.
A further object of the invention is to drill a plurality of wells within the confines of a single drilling structure without requiring complete redundancy of equipment for each well drilled concurrently. That is, in the preferred form of the invention, major items of equipment may be devoted on a time shared basis to the various wells concurrently drilled as these wells require the use of such equipment. By utilizing said major items of equipment on such such a time shared basis, substantial savings are achieved in connection with the equipment that must dedicated for use in drilling a particular well. Most significant in this regard is the use of a master drilling draw works, which is used to draw drilling pipe from wells in stands of pipe, each stand representing a plurality of linearly joined sections of drilling pipe. In conventional practice, on the other hand, the derrick associated with each individual well is of a height and structural capability to withdraw a stand of pipe in order to change drill bits. Thus, in conventional practice the concurrent drilling of four different well requires the construction of four derricks, each associated with a separate one of the wells, and each capable of withdrawing a stand of pipe. In contrast, however, according to the present invention, a single master drilling draw works is provided and is used on a time shared basis to withdraw stands of pipe from wells as drill bit changes are required in connection with the pipe being used to drill each of the wells. This allows a much smaller draw work assembly to be used with each of the rotary drilling tables to perform the more frequently required function of feeding additional drill sections of pipe into the well as the well is drilled deeper and deeper.
Another object of the invention in its land based application is to provide a well drilling structure that is acceptable to govermental authorities and not objectionable to surrounding inhabitants for drilling wells in urbanized areas. The confinement of drilling operations to a small area and the location of the drilling structure within an aesthetically compatible facade allows drilling to proceed in urbanized areas where drilling would otherwise be entirely unacceptable to surrounding community.
A further object of the invention in connection with the land based application of the well drilling apparatus of this invention is to provide a well drilling system which is entirely enclosed within a structure having verticallly extending walls that rise from the drilling floor and surround and encase all of the necessary equipment. Such a structure is most useful in guarding against theft and vandalism. The security provided by the enclosure and the confinement of the drilling equipment to a relatively small and protected area adds further to the economic attractiveness of the utilization of the invention disclosed herein.
Yet another object of the invention is the confinement of the surface area of the fluidized mineral production field to a few hundred square feet, in contrast to conventional land based drilling fields which extend over many square miles. A producing complex that covers the same subsurface area as a conventional oil field, but which is concentrated at the surface by virtue of slant drilling techniques into a small enclosed area reduces substantially the installation cost, and the cost of maintenance and operation of oil and gas gathering lines. The probability of line breakage and oil spills is likewise reduced. Furthermore, since the entire surface complex is enclosed within a single large structure, means for containing spills are easily made a part of the design so that pollution of the environment is averted.
An additional advantage of the invention as applied to drilling at the floor of bodies of water is that the housing for the invention may be constructed to initially float in water. Thus, the structure may be floated on the surface of the body of water to a drilling cite where a plurality of wells are to be drilled concurrently at the sea floor of the body of water from within the structure. One end of the structure may be filled with water so that end sinks towards the floor of the body of water thereby orienting the structure vertically as it descends. Water may be continued to be introduced into the sinking end of the structure until that end reaches the floor of the body of water. The height of the structure, should be designed so that the structure extends from the floor to surface of the body of the water. The hollow structure may be secured in position at the floor of the body of water by pouring a material, such as concrete, into or around the sunken end of the structure to hold it in position. Llateral protuberances from the structure may be employed to assure bonding of the concrete to the walls of the structure. The foregoing concept of caisson deployment is explained at greater length in U.S. patent application Ser. No. 581,936, filed on May 29, 1975.
Once the sunken end of the structure is secured in position at the floor of the body of water, a bottom seal is formed across the interior of the sunken end of the structure. Water is pumped out from within the structure and thereafter the structure is maintained in a relatively water free condition. Of course it is to be understood that minor leaks will invariably occur, and a pumping system should be utilized to ensure that the structure is indeed maintained water free.
It is essential that the sunken end of the structure be secured in position on the floor of the body of water prior to evauation of the water from within the structure, as the water free condition of the structure produces a strong tendency for the surrounding sea water to push the structure up toward the surface.
Several significant advantages are provided by utilizing the hollow water free structure of the invention. The well drillling apparatus of this invention as applied to offshore driling minimizes the adverse consequences that can occur if oil escapes from the wells in the floor of the sea bottom. This is because escaping oil will be confined within the vertically extending walls, and so cannot cause ecological damage. Furthermore oil well fires are easily extinguished, since the drilling surface is located far below the water level surface at the exterior of the structure. Thus, the provision of inlets provides a ready supply of water to extinguish any fires that might break out.
Another problem that occurs with conventional offshore drilling apparatus is that heavy seas and weather conditions reduce drilling activity by personnel aboard semi-submersible floating platforms and platforms supported on leg structures to an absolute minimum. This materially adds to the time required to complete the drilling operations and bring the wells into a producing capability.
In one broad aspect the present invention is a well drilling apparatus located within a confining structure having vertically extending walls rising from a drilling floor and enclosing: a plurality of rotary drilling tables laterally displaced from each other proximate to the drilling floor. Each of the rotary drilling tables is arranged to accomodate a separate drilling assembly, which assembly includes drilling pipe for drilling separate wells at spacially separate locations at the drilling floor. Separate drilling draw work assemblies are likewise associated with and mounted in vertical displacement from each of the rotary drilling tables. These separate drilling draw work assemblies are used for manipulating the drilling pipe and other portions of the drilling assembly utilized with the associated rotary table.
While utilizing rotary drilling tables, mud pumps, shaker tables, tanks, and draw works of conventional design, the invention resides in the relocation of the pieces of equipment and the addition of necessary equipment to achieve multiple drilling capablity within a confined area and without complete cross section throughout the height of the confining structure of the well drilling apparatus of the invention, there is ample room for a multiplicity of drilling draw works.
While these draw works are of a conventional design, there arrangement and positioning radically departs from the arrangements heretofore employed. More specifically, the draw works of the present invention are repackaged into a bridge crane type of mechanism and are relocated from their conventional position on the drilling platform to an overhead traveling mechanism. If a tall structure is used that contains a master drilling draw work assembly in addition to the draw works separately associated with each drilling table, a minimum height for the bridge mounting of the separate draw works is on the order of 45 feet. This allows enough room to install additional sections of drilling pipe as the hole is deepened using the draw works dedicated for use with a particular rotary table. These dedicated draw works, however, are used only for drilling the well. A single master draw work assembly is located in the upper portion of the structure above the upper extremity of any of the separate dedicated draw works, and is used to pull pipe from the hole of the well when it is necessary to change bits or conduct bottom hole operations. A conventional derrick pulls three joints of drilling pipe at a time, about 90 feet. Thus, if a well is at a 9,000 foot depth, 100 stands of pipe would have to be removed from the hole and leaned against the side of the derrick for temporary storage. In the apparatus of the present invention, on the other hand, the confining structure with upright vertical walls rising from the drilling floor is about 300 feet high. Each stand of pipe may therefore be about 240 feet long so that it would be necessary to draw only 38 stands of pipe and hang them in temporary storage for the same 9,000 foot well. This represents a 62% savings in both time and manpower.
If desirable, the height of the confining structure of the invention can be limited to that of a conventional derrick, about 140 feet. The master draw works would then be at an equivalent height to the normal crown blocks in the derrick and would also hoist the 90 foot stand of drilling pipe and would require and equivalent amount of manpower and time to extract pipe from a well, change bits or perform other bottom hole operations, and replace the pipe in the well. However, a substantial savings in manpower and equipment is still available since the same master draw works can be used in association with a plurality of well holes.